The present invention relates generally to a planar array type microwave antenna for use in, receiving, for example, a satellite broadcast and more particularly to a microwave antenna structure.
In the art, a circular polarized wave planar array antenna has been previously proposed, namely, a suspended line feed type planar antenna in which a substrate is sandwiched between metal or metallized plastic plates having a number of spaced openings forming a part of radiation elements, a pair of resonance probes which are perpendicular to each other and the number of which corresponds to a number of spaced openings are formed on a common plane and signals fed to the pair of resonance probes are mixed in phase within the suspended line (in our co-pending U.S. patent applications Ser. No. 888,117 filed on July 22, 1986 and Ser. No. 058,286 filed on June 4, 1987).
It is desirable that the above-mentioned planar antenna be reduce in thickness as compared with the existing one, and also its mechanical configuration can be simplified. Further, it is desirable to use an inexpensive substrate readily available on the market for high frequency use, achieving antenna gain equal to or larger than that of the previous planar antenna which uses an expensive microstrip line substrate.
The suspended line can achieve such advantages that it forms a low loss line as a circuit for feeding the planar antenna and also that it can be formed on an inexpensive film-shaped substrate. Further, since this conventional planar antenna utilizes a circular or rectangular waveguide opening element as a radiation element it is possible to construct an array antenna which has small gain deviation over a relatively wide frequency range.
Meanwhile, a patch type microstrip line antenna element is proposed in order to reduce the thickness of the planar array antenna. Also, this patch type microstrip line antenna can be made high in efficiency, wide in band width by effective use of the advantages of the suspended line and the thin radiation element, and it can be reduced in thickness and in weight at the same time as is disclosed in our co-pending U.S. patent application Ser. No. 223,781, filed July 25, 1988.
In a suspended line feed type planar array antenna in which a substrate is sandwiched between a pair of metal or metallized plastic plates, the resonance type printed patch radiators are formed on the substrate at positions corresponding to slots formed through one of the metal or metallized plastic plates to thereby form the planar antenna.
However, in the planar array antenna disclosed in our co-pending U.S. patent application Ser. No. 233,781, a number of resonance type printed patch radiators have flanges formed therearound as supporting portion so that upon manufacturing, a cutting treatment becomes necessary. Thus, it cannot be mass-produced efficiently and also it is increased in cost.